OpenSMTPD

OpenSMTPD: A Secure SMTP Server Implementation

OpenSMTPD is a free and open-source implementation of the server-side SMTP protocol, as defined by RFC 5321 with some additional standard extensions. This project allows ordinary machines to exchange emails with other systems speaking the SMTP protocol. Started out of dissatisfaction with other implementations, OpenSMTPD is a fairly complete SMTP implementation.

Main Features

• A secure and reliable implementation of the SMTP protocol
• Supports various authentication mechanisms, including SASL, STARTTLS, and AUTH
• Can be used as a drop-in replacement for existing SMTP servers
• Highly configurable and extensible through its modular design
• Written in C, making it highly portable and efficient
• Licensed under the ISC license, allowing for free use and re-use by everyone

With OpenSMTPD, you can trust that your email server is secure and reliable, providing a robust foundation for your email infrastructure. Whether you're looking to replace an existing SMTP server or set up a new one, OpenSMTPD is an excellent choice.